The present disclosure relates to a detection-cord attachment device, in particular for an overheating and leak detection system in an aircraft.
Such systems, often abbreviated to OHDS (overheating detection system), are used to detect and locate local temperature increases (overheating) due to accidental leaks in gas pipes carrying hot gases taken from the engines of the aircraft to other parts of the aircraft. The detection cords are mounted on attachment devices provided along the gas pipes.
In a known design, the attachment devices include brackets for thermal-detection cords (for example eutectic cords) provided with slots into which the cords, surrounded by a coil of isolating material (such as silicone), are placed, and closings (collars, clamps or attachment clips) that are subsequently closed on the brackets and screwed down such as to clamp the cords and hold same in the slots. The flexible silicone coils absorb the deformations caused by clamping and isolate thermal-detection cords from the metal elements of the attachment device.
FIG. 1 shows an existing example of an overheating detection system in which a pressurized stream of hot gas is drawn from the jet engines 1 via pipes 2 extending along the wings and the fuselage, before being carried to the actuators 3. The valves 4 installed on the pipes 2 regulate the gas flow rates in the pipes 2. These valves also enable certain portions of the pipes 2 to be isolated in the event of a gas leak. The overheating detection system includes cords 5, arranged in loops, that extend along the pipes 2. An electrical signal runs through the cords 5. The cords 5 are eutectic cords comprising a core (water+salt mix) designed or configured to melt when they come into contact with the hot gas leaking out of the pipes 2. The modification of the structure of the core of the cord 5 locally modifies (at the location of the leak) the electrical resistance of the cord and therefore the electrical signal running through the cord. This modification is detected, thereby identifying the zone.
FIG. 2 shows that the cords 5 are attached close to the pipes 2 by attachment devices 6 arranged in places. In practice, the pipes 2 are covered with isolating glass wool to prevent heat losses and an outer metal cover, or a flexible isolation sleeve on the connections between pipes 2. This cover or this sleeve is provided with ventilation holes 7 through which the gas leaking from the pipes 2 can escape. Placing the cords 5 in front of the ventilation holes 7 enables leaks to be detected.
In a conventional design, shown in FIG. 3, the attachment devices 6 are mounted on metal butterfly brackets 8 installed on the outside of the pipes 2, the isolating lining 9 of same and the metal cover 10 of same. The attachment devices 6 each include a bracket 11 mounted on the metal butterfly bracket 8 using a bolt 12 and a spacer 13 holding the bracket 11 at a given distance from the metal butterfly bracket 8 and from the duct 2. The bracket 11 includes a lower cradle 14 designed or configured to include two slots 16 opening out onto the side opposite the pipe 2. The cords 5 are placed in the slots 16, and the slots 16 of a given bracket 11 receive two portions of cords 5. To effect clamping, these portions of cords 5 are surrounded by flexible coils 15, and it is these coils 15 that are clamped. Closings 17 are used for this purpose, articulated at the sides of the cradle 14 using hinges 18 and held in place using attachment screws 19. The drawbacks of this attachment device 6 are a degree of complexity of the bracket 11 and the need to use attachment screws 19 to clamp the cords 5. A tool is therefore required for clamping.
Such devices present assembly issues, in particular installing the coils with the required degree of precision, or reaching some of the brackets with the tools required to clamp the closings in restricted or difficult-to-access areas, such that the attachment devices are not always properly closed, and support points can become detached, and in any case the complexity of the assembly makes assembly relatively slow and difficult, even when it is completed successfully.
It is intended to improve such attachment devices by replacing the known bracket with another, such as to guarantee precise mounting of the cords in less time and without using tools to install the cords fitted with coils.